The present invention relates to stimulation systems and, more particularly, systems for transcutaneously charging and communicating with a body-implanted stimulator having a rechargeable battery.
Radio-frequency powered implantable stimulators and battery powered, implantable microstimulators are described in the art. See, for instance, U.S. Pat. No. 5,193,539 (“Implantable Microstimulator); U.S. Pat. No. 5,193,540 (“Structure and Method of Manufacture of an Implantable Microstimulator”); U.S. Pat. No. 5,312,439 (“Implantable Device Having an Electrolytic Storage Electrode”); U.S. Pat. No. 6,185,452 (“Battery-Powered Patient Implantable Device”); U.S. Pat. Nos. 6,164,284 and 6,208,894 (both titled “System of Implantable Device for Monitoring and/or Affecting Body Parameters”). The '539, '540, '439, '452, '284, and '894 patents are incorporated herein by reference in their entireties.
Microstimulators to prevent or treat various disorders associated with prolonged inactivity, confinement or immobilization of one or more muscles are taught, e.g., in U.S. Pat. No. 6,061,596 (“Method for Conditioning Pelvis Musculature Using an Implanted Microstimulator”); U.S. Pat. No. 6,051,017 (“Implantable Microstimulator and Systems Employing the Same”); U.S. Pat. No. 6,175,764 (“Implantable Microstimulator System for Producing Repeatable Patterns of Electrical Stimulation”); U.S. Pat. No. 6,181,965 (“Implantable Microstimulator System for Prevention of Disorders”); U.S. Pat. No. 6,185,455 (“Methods of Reducing the Incidence of Medical Complications Using Implantable Microstimulators”); and U.S. Pat. No. 6,214,032 (“System for Implanting a Microstimulator”). The '596, '017, '764, '965, '455, and '032 patents are incorporated herein by reference in their entireties.
Implantable stimulators having rechargeable batteries have specific requirements. In general once a stimulator is implanted within a patient's body, it is intended to stay there permanently. When a rechargeable battery is used to power an implantable stimulator, there must be a transcutaneous means to recharge the rechargeable battery in the stimulator without explanting the stimulator. In addition, there must also be a means to communicate with the stimulator after it has been implanted in order to transmit and receive control signals from and to the stimulator, as well as to transfer data from and to the stimulator. An important technical issue is how a rechargeable battery in an implanted stimulator may be revived when the rechargeable battery is completely depleted, i.e., to zero volts.
A specific form of an implantable stimulator is a microstimulator. Microstimulators present advantages over conventionally sized stimulators in that microstimulators are more easily implanted, with less surgical trauma. Advantageously, microstimulators may be injected through a large bore needle or placed via a small incision in the skin. In addition, microstimulators may be implanted in locations that do not offer enough space to contain larger, conventional-sized stimulators and their associated extension leads.
One application that is particularly suited for using a microstimulator is the treatment of urinary urge incontinence. The BION™ microstimulator is currently being used in patients to treat urinary urge incontinence by stimulating the pudendal nerve. In prior art implantable systems for treating incontinence, a conventional-size stimulator is attached to a lead having an electrode or electrodes on the distal lead tip. The lead, having a substantial length, can be tunneled to the target nerve deep inside the body, while the conventional-sized stimulator can remain implanted just beneath the surface of the skin. Because the conventional stimulator is intended to be placed just below the surface of the skin, the technical requirements for designing a telemetry communication system using such a conventional stimulator is, relatively speaking, easier to accomplish. Moreover, because the conventional-sized stimulator is in a comparatively large housing, such a stimulator can contain a primary, one-time-only-use battery and thus, no recharging is required.
An implantable microstimulator, in contrast, generally does not use an extension lead, as the electrodes are often placed directly on the body of the microstimulator. Because the electrodes are placed on the body of the microstimulator, it must usually be placed very close to the target tissue (usually a nerve) being stimulated. In the case of the urinary incontinence application, therefore, the microstimulator is implanted deep inside the body near the pudendal nerve and not, as in the case with conventional stimulators, just below the surface of the skin. In addition, when a microstimulator is used, the small housing puts the use of space at even a greater premium and effectively prohibits the use of a primary battery and, instead, necessitates the use of a rechargeable battery.
Thus, the technical challenges presented by a microstimulator that is implanted deep in the body are highly complex because (a) the microstimulator uses a rechargeable battery and (b) the microstimulator can be implanted more deeply and at variable depth within the body than a conventional stimulator. The variability of implantation depth can be problematic because the components that are used to charge the battery and communicate with the stimulator must accommodate this variability. Consequently, the technical requirements needed to fulfill the dual operations of transcutaneously recharging a battery and communicating with an implantable microstimulator are more daunting than using a conventional implantable stimulator, which merely requires near-distance telemetry communication and no charging circuitry. There are additional technical challenges to overcome when a microstimulator is placed deep in the body, for instance, in the lower part of the torso, as is the case for the urinary incontinence application. In particular, the external device configuration or configurations must be determined which can best recharge the battery in the microstimulator and communicate with the microstimulator. This set of technical requirements presents unique challenges in designing a charging and communication system which the present novel invention addresses.